Happy to see someone applying some science to our field instead of just going with a hunch. That said, as kortilla already mentioned, in most cases 3 months is

Happy to see someone applying some science to our field instead of just going with a hunch. That said, as kortilla already mentioned, in most cases 3 months is too short time to get a complete answer. IIRC "Principles of Network and System Administration" by Mark Burgess has more about it, but intuitively you have to look for the largest cycles that exist, but there is also, again as mentioned by kortilla, events that doesn't happen on a schedule. One thing I try to do is, when I come across code that I have to research is to write down in the documentation for the function (Javadoc or similar) why it exist and the conditions when it can be deleted. You can also try to add some instrumentation code that notifies you when something is called. That way you can end up like me who, every new years day get a weird sms message at 14:00 or 14:01 from a system that no one can find, but at least I know that some system I cannot remember anymore still runs somewhere :-)